Large vessels are used in many industries during the manufacturing, processing and distribution of numerous types of products. It is a well-accepted fact that these vessels must be cleaned on a regular basis in order to safeguard product quality and purity.
In order to effectively and economically clean such vessels clean-in-plane (CIP) systems have been developed and relied upon. Such systems eliminate the need for process equipment in large scale plants from having to be disassembled whenever sterilization and cleaning are required.
There are four factors that are critical and must be optimized to minimize both monetary costs and environmental costs in a properly managed CIP process. These factors are:
Time
Temperature
Mechanical Action
Chemical Activity
The total of these factors adds up to 100%. Therefore, one factor can be lessened and another increased to keep the total at 100%.
Time: With respect to the time element, some solids and liquids may be quite soluble while others are quite insoluble in the cleaning solution used. As a result the wash time will need to be varied depending on the application.
Temperature: Generally speaking, increasing the temperature of the cleaning solution will increase the rate of dissolution and therefore reduce cleaning time and water consumption.
Mechanical Action: Water for cleaning the tanks is normally introduced through a spray device. There are various kinds of spray devices that operate at varying pressures so that turbulence occurs in the water and in the water film on the surface being cleaned. As the pressure is increased, the impingement force and turbulence of the cleaning fluid goes up, improving the scrubbing action and reducing cleaning time and water consumption.
Chemical Activity: Cleaning chemicals such as detergents, caustics and acids are sometimes used to enhance the cleaning activity. The more aggressive the cleaning solution, the less time required to clean contaminated surfaces.
Once the CIP process has been worked out, then time, temperature, mechanical activity and chemical activity must be validated with each CIP process in order to assure that the desired cleaning cycle was performed. If any one factor fails to meet specified values then the expected cleaning did not take place.
The common presently used method of cleaning process tanks or vessels involves spraying the interior of the vessel with cleaning solutions. Examples of tank cleaners may be found in U.S. Pat. Nos. 6,123,271 and 5,954,271.
Referring to FIGS. 1A, 1B and 1C which represents a conventional system, it can be seen that the cleaning solution enters the device at the inlet causing the device to rotate about axis A1 (FIG. 1B) as well as about axis A2 (FIG. 1C) and exits the device through nozzles 106 located on axis A1. The nozzles are selected based on the size of the tank being cleaned, the product being removed, the available pressure and flow rate of cleaning solution, and jet stream parameters.
As is the case with a home dishwasher, the cleaning solution may be re-circulated during the cleaning operation. However, unless the solution is cleaned between uses the cleaning solution will likely contain foreign materials that can clog or damage the nozzle.
If a nozzle were to clog, then:
1) the flow of cleaning solution through the nozzle would be reduced or totally blocked,
2) the parameters of the nozzle jet stream could be dramatically altered,
3) the nozzle would not clean as expected,
4) the cleaning device as a sum of all nozzles would not be operating as required to clean the tank.
If, on the other hand, a nozzle were to open up, then:
1) the flow of cleaning solution thru the nozzle would increase possibly reducing flow and pressure to the remaining nozzles,
2) the parameters of the nozzle jet stream could be dramatically altered,
3) the failed nozzle would not clean as expected,
4) the cleaning device as a sum of all nozzles would not be operating as required to clean the tank.
The present invention is directed toward a method of for monitoring individual nozzle performance and detecting when a nozzle becomes clogged or enlarged.
German patent DE 29919445 suggests that if there are at least two alternating jets in a dishwasher machine, then the jet armature rotation sensor can be designed in such a way that it can, depending on the expected frequency spectrum of the spray striking the sensor wall, detect which jet is blocked in its rotational movement. Assuming this patent defines a “jet” as being a single spray nozzle on the “jet armature” (as opposed to one of several jet armatures) then it is accepted that a dishwasher wall may be designed to vibrate differently depending on where it is struck by the jet spray. That being the case, then in order to identify individual nozzles, an armature must be designed to direct each nozzle to unique positions on the sensor wall. The sensing electronics would then detect the presence of each unique frequency signature. There are, however, a number of problems with this design
First, the rotating arm and sensing wall must be especially designed to work together to generate the unique spectrums for each and every nozzle. This is possible for the invention taught in the German patent since they are designing and building an entire new product. In the tank cleaning industry this is not possible since an endless array of tanks are being cleaned by an ever widening assortment of tank cleaners. It is not possible to generate unique frequency signatures for each individual nozzle on a tank cleaner.
Second, the approach shown by the German patent requires that the processing electronics evaluate and detect “specific frequency signatures” unique to each nozzle. As the number of nozzles increases the task of identifying unique signatures becomes very complicated and costly.
Even further, the approach shown in the German patent “detects which jet is blocked in its rotational movement”. It does not detect partially blocked, eroded or damaged nozzles. The present invention teaches an improved method of detecting clogged nozzles that is not related to the frequency signature of nozzles, does not require special preparation to the rotating arm or the sensing wall, can be applied to any number of rotating nozzles and is capable of detecting nozzle performance ranging from fully clogged, to enlarged.
There is another very important drawback to the approach in the German patent. It was designed for use in systems where the spray nozzles rotate in a fixed path. This is necessary in order to direct each nozzle to a unique position along the sensing wall, see FIG. 2.
In dual axis systems, each nozzle sprays the entire inner surface of the tank. For example, referring to FIG. 3, the spray jet from each nozzle travels from the top of the tank downward along the side wall until it reaches the bottom. It then travels a short distance along the bottom, turns and proceeds upward along the opposite side wall until it reaches the top of the tank. The pattern resembles a FIG. 8. With the completion of each pass, the FIG. 8 spray pattern rotates slightly causing the spray to take a parallel but different path with each successive pass. Eventually the spray pattern rotates a full 360 degrees causing every nozzle to spray the entire inner surface of the tank. (See FIGS. 4a and 4b.) Thus, it would not be possible restrict a particular nozzle to a specific area of the tank wall.
In U.S. Pat. No. 5,681,401 to Maytag, it is suggested that a reduction in the signature frequency may indicate a blockage. FIG. 5 shows a comparison of two time series. FIG. 5A represents the sound signature acquired from a single armature dishwasher. FIG. 5B represents the sound signature from a three nozzle dual axis spray cleaner. Each peak shown in FIGS. 5A and 5B represents the vibrations captured by the sensor as the spray passed the sensing area.
An examination of FIG. 5A shows that the peak to peak amplitude of each nozzle is more or less the same amplitude. The frequency of the spray signature is the frequency of the time series consisting of combined nozzle spray peaks. If one of the two nozzles were to clog, then every other peak would be eliminated and the frequency of the time series would be one-half of the original. Thus a blocked nozzle would indeed result in a change in frequency. On the other hand consider the case where the nozzle armature for one reason or another slows to one-half of its original velocity. The resultant time series would then be one-half of its original frequency. Based on the foregoing assumption, the change in frequency would be falsely interpreted as a blocked nozzle. The fact is, basing blocked nozzle detection on the spray signature frequency is very unreliable. The signature frequency can be affected by many things, some of which are normal and some of which may not be so normal.
For example, an examination of the time series in FIG. 5A shows a wide variation in peak to peak amplitude. Based on the above hypothesis we must conclude that one or more of the spray nozzles are experiencing a blockage. Such a conclusion, however, would be false. The fact is the tank cleaner shown in FIG. 5A is operating perfectly normally. Given that all of the spray nozzles are identically the same, are operating properly, have no blockage, and have equal flow and pressure, why then are the peak to peak amplitudes significantly different. The answer lies in the fact that the intensity of the vibrations received by the sensor is not solely a function of the impingement force but is also a function of the displacement between the impingement location and the sensor. FIG. 6 shows a typical relationship between impingement displacement and attenuation of the impact induced vibrations in the tank wall. From FIG. 6 we note that the vibrations are a maximum when the spray jet impacts the area directly under the sensor and decrease as displacement increases.
In the case of single axis cleaners, the spray jet follows the same path each and every revolution. This results in a constant impact displacement and a constant peak to peak attenuation. On the other hand, the spray path of the multiple axis tank cleaners changes with every rotation causing peak to peak variations in the impact displacement and peak to peak amplitude. Thus the hypothesis set forth in the Maytag patent does not apply in the case of multiple axis systems.
The present invention does not utilize frequency changes of the spray signatures to detect nozzle blockages. Instead this invention teaches to separate and measure the impingement force associated with each spray nozzle. Variations due to impingement displacement are removed by averaging impingement force over many passes.